Quantitative Biology > Neurons and Cognition

Title:Computation of Object Approach by a Biophysical Model of a Wide-Field Visual Neuron: Dynamics, Peaks, and Fits

Abstract: Many species show avoidance reactions in response to looming object
approaches. In locusts, the corresponding escape behavior correlates with the
activity of the lobula giant movement detector (LGMD) neuron. During an object
approach, its firing rate was reported to gradually increase until a peak is
reached, and then it declines quickly. The ETA-function predicts that the LGMD
activity is a product between an exponential function of angular size and
angular velocity, and that peak activity is reached before time-to-contact
(ttc). The ETA-function has become the prevailing LGMD model because it
reproduces many experimental observations, and even experimental evidence for
the multiplicative operation was reported. Several inconsistencies remain
unresolved, though. Here we address these issues with a new model (PSI-model),
which explicitly connects angular size and angular velocity to biophysical
quantities. The PSI-model avoids biophysical problems associated with
implementing exp(), implements the multiplicative operation of ETA via divisive
inhibition, and explains why activity peaks could occur after ttc. It
consistently predicts response features of the LGMD, and provides excellent
fits to published experimental data, with goodness of fit measures comparable
to corresponding fits with the ETA-function.

Comments:

A revised version of this paper with the title "Emergence of Multiplication in a Biophysical Model of a Wide-Field Visual Neuron for Computing Object Approaches: Dynamics, Peaks, & Fits" has been accepted in Advances in Neural Information Processing Systems, NIPS 2011, Granda, Spain